It is well known to those skilled in the art that polyurethane and polyisocyanurate foams can be prepared by reacting and foaming a mixture of ingredients, consisting in general of an organic polyisocyanate (including diisocyanate) and an appropriate amount of polyol or mixture of polyols in the presence of a volatile liquid blowing agent, which is caused to vaporize by the heat liberated during the reaction of isocyanate and polyol. It is also well known that this reaction and foaming process can be enhanced through use of amine and/or tin catalysts as well as surfactants. The catalysts ensure adequate curing of the foam while the surfactants regulate and control cell size.
In the class of foams known as low density rigid polyurethane or polyisocyanurate foam the blowing agent of choice has been trichlorofluoromethane, CCl.sub.3 F, also known as CFC-11. These types of foams are closed-cell foams in which the CFC-11 vapor is encapsulated or trapped in the matrix of closed cells. They offer excellent thermal insulation, due in part to the very low thermal conductivity of CFC-11 vapor, and are used widely in insulation applications, e.g. roofing systems, building panels, refrigerators and freezers. Generally, 1-40 and typically, 15-40 parts of blowing agent per 100 parts polyol are used in rigid polyurethane or polyisocyanurate formulations.
Flexible polyurethane foams on the other hand are generally open-cell foams and are manufactured using a diisocyanate and polyol along with catalysts and other additives with various combinations of water, methylene chloride and CFC-11 as the blowing agent. These foams are widely used as cushioning materials in items such as furniture, bedding and automobile seats. The quantity of CFC-11 used as an auxiliary blowing agent in flexible foam manufacture varies from 1-30 parts by weight per 100 parts of polyol according to the grade of foam being prepared.
It is common practice in the urethane foam systems area to prepare so-called pre-mixes of certain components used to prepare the foam, i.e. often the appropriate quantities of polyol, blowing agent, surfactant, catalyst, flame retardant and other additives, are blended together and sold along with the stoichiometric quantity of polyisocyanate component in two separate containers. This is convenient for the end user who then only has to combine the two reactants in order to create a foam. It is also common practice for large foam manufacturing plants to pre-mix the polyol with the blowing agent in bulk storage containers. This liquid mixture possesses a lower viscosity than the pure polyol and is therefore easier to pump and meter into the mixing zone of the foam manufacturing equipment.
Special precautions must be taken when following these practices if the blowing agent is CFC-11, namely, the CFC-11 must have a stabilizer added to it in order to inhibit a reaction which can occur between the fluorocarbon and the polyol resulting in the production of acids such as hydrogen chloride and other organic products such as aldehydes and ketones. These reaction products have a detrimental effect on the reactivity characteristics of the foam ingredients which in the worst case results in no foaming action at all. Stabilizers found useful in stopping the reaction between fluorocarbon and polyol have been disclosed, for example, in U.S. Pat. Nos. 3,183,192 and 3,352,789. Use of such stabilizers with CFC-11/polyol based blends, although successful when measured in terms of fluorocarbon stability, have disadvantages such as added expense and sometimes cause odor problems which persist even in the finished foam.
For the above reasons, it would be advantageous to identify useful fluorocarbon blowing agents which do not require stabilizers in the presence of polyols. Unfortunately, there does not appear to be any reliable scientific basis upon which to predict such stability.
The propensity for a fluorocarbon species to react with an OH containing species, like a polyol, is dependent, in the fundamental sense, on the electronic and molecular structures of the fluorocarbon and the OH species involved. Studies of certain reactant systems, such as CFC-11 and ethanol by P.H. Witjens. Aerosol Age Vol. 4. No. 12 (December 1959). P.A. Sanders "Mechanisms of the Reaction Between Trichlorofluoromethane and Ethyl Alcohol", Proc. of the CSMA 46th Mid-Year Meeting, (May 1960), and J.M. Church and J.H. Mayer, J. of Chem. and Eng. Data, Vol. 6 No. 3 (JuIy 1961), have shown that the reaction products include hydrochloric acid acetaldehyde CHCl.sub.2 F. Sanders, in Soap and Chemical Specialties, (December 1965) has shown that these reactions are further promoted by the presence of metal and water.
H.M. Parmelee and R.C. Downing in Soap Sanitory Chemicals, Vol. 26, pp. 114-119 (July 1950) have shown that fluorocarbons such as chlorodifluoromethane (FC-22). 1,1-difluoroethane (FC-152a). 1,1,1-chlorodifluoroethane (FC-142b) and 1,1,2,2-tetrafluoro-1,2-dichloroethane (FC-114) undergo reactions in aqueous and ethanol and isopropanol solutions in the presence of steel and aluminum. Church and Mayer, supra, state that mixed polyhalogenated hydrocarbons containing both chlorine and fluorine on the same carbon atom are less stable than the polyfluoro derivatives.
The molecular structure of FC-141b (CCl.sub.2 FCH.sub.3) suggests that CFC-141b is amenable to dehydrochlorination due to the presence of hydrogen and chlorine atoms on adjacent carbon atoms. On the other hand CFC-123 (CHCl.sub.2 CF.sub.3) is amenable to dehydrofluorination, a process requiring a greater activation energy. Therefore it would be expected that CFC-141b would be less stable than CFC-123.
The prior art evidence therefore suggests that chlorine and fluorine substituted hydrocarbons as a class react with organic OH containing species such as alcohols and polyols.
U.S. Pat. No. 4,076,644 discloses that CFC-123 may be used as a blowing agent and does not require a stabilizer in the presence of polyols. Thus. CFC-123 may be an exception to the rule that fluorocarbons require stabilizers.
However, stability tests on CFC-123 in the of a variety of polyols show that CFC-123 may not be stable in the presence of some polyols which are commonly used in the preparation of polyurethane and polyisocyanurate foams.
It is accordingly an object of this invention to identify another fluorocarbon useful as a blowing agent for polyurethane and polyisocyanurate foams which is stable in the presence of polyols.
It is another object of this invention to identify such a fluorocarbon which is also considered to be a stratospherically safe substitute for CFC-11 which is thought to be a contributor to ozone depletion and global greenhouse warming.
Yet another object of the invention is to identify such a fluorocarbon which may have a wider or at least different range of applicability to polyols than does CFC-123.
Other objects and advantages of the invention will be apparent from the following description.